function createREQ() 
{
	try 
	{
  	req = new XMLHttpRequest(); /* p.e. Firefox */
  } 
  catch(err1) 
  {
  	try 
  	{
    	req = new ActiveXObject('Msxml2.XMLHTTP'); /* algunas versiones IE */
    } 
    catch(err2) 
    {
			try 
			{
      	req = new ActiveXObject("Microsoft.XMLHTTP"); /* algunas versiones IE */
      } 
      catch(err3) 
      {
      	req = false;
      }
		}
	}
  return req;
}

function requestGET(url, query, req) 
{
	myRand=parseInt(Math.random()*99999999);
	req.open("GET",url+'?'+query+'&rand='+myRand,true);
	req.send(null);
}

function requestPOST(url, query, req) 
{
	
	req.open("POST", url,true);
	req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
	req.send(query);
}

function doCallback(callback,item) 
{
	eval(callback + '(item)');
}

function doAjax(url,query,callback,reqtype,getxml) 
{
	// crea la instancia del objeto XMLHTTPRequest 
	
	var myreq = createREQ();
	myreq.onreadystatechange = function() 
	{
		if(myreq.readyState == 4) 
		{
   			if(myreq.status == 200) 
   			{
      			var item = myreq.responseText;
		      	if(getxml==1) 
      			{
        			item = myreq.responseXML;
      			}
      			doCallback(callback, item);
    		}
  		}
	}

	if(reqtype=='post') 
	{
		
		requestPOST(url,query,myreq);
	} 
	else 
	{
		requestGET(url,query,myreq);
	}
}